1. Field of the Invention
The present invention relates to a lens having broadband anti-reflective nanostructures formed using nano-island masks and a method for making the same, and more particularly to a lens having broadband anti-reflective nanostructures formed using nano-island masks and a method for making the same, in which nanostructures having a size and period equal to or smaller than the light wavelength are formed on the surface of a lens to obtain a lens having decreased reflectance, increased transmittance and high efficiency.
2. Description of the Related Art
As used herein, the term “microlens” refers to a lens having a diameter ranging from about 1 μm to a few mm. The microlens is used as an optical device in the fields of telecommunication devices, medical devices, optical sensors and photoelectric devices, which include connections between optical devices such as planar lightwave circuits (PLCs), laser diodes (LDs) and photodiodes (PDs). Such microlenses can be classified into gradient index lenses, spherical surface microlenses, array lenses, Fresnel lenses and the like, and are made by a method such as molding, ion exchange, diffusion polymerization, sputtering or etching.
In addition, the microlenses are necessarily used for the purpose of increasing the light-receiving efficiency of image sensors, such as CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor), by using the light-receiving characteristics of the microlenses. These microlenses are made by a thermal reflow or resist melting method based on the thermoplastic properties of polymer materials. The reflection of light resulting from the difference in refractive index between the microlens and air reduces the light-gathering efficiency of the microlens.
Generally, high-transmittance lenses having low reflectance compared to microlenses are made using anti-reflective coating. In a known method for making a high-transmittance lens, an anti-reflective film consisting of a multilayer structure of an oxide layer, a nitride layer and the like is formed on the surface of a microlens. The anti-reflective film serves to increase the light transmittance of an optical device while reducing the light reflectance.
However, this anti-reflective coating technology according to the prior art has shortcomings in that the anti-reflective film becomes mechanically unstable as temperature changes, it is difficult to find a coating material suitable for the intended use, and the cost of the coating material is expensive to increase the production cost. In addition, the method for forming the multilayer anti-reflective film has problems in that it requires a special medium having a very low refractive index and employs a complex process, and thus the overall efficiency of the process is reduced.
Accordingly, there has been an increasing demand for new technology for the above-described conventional anti-reflective coating technology, and according to this demand, technology for forming an anti-reflective structure was suggested as an alternative for the conventional anti-reflective coating technology. In other words, the technology for forming the anti-reflective structure has advantages over the conventional anti-reflective coating technology in that the anti-reflective structure can be made at a relatively low cost, can be used in a wider wavelength range and can provide anti-reflective effects over a wider incident angle.
Examples of conventional methods for forming this anti-reflective structure include a lithography-based method. However, this method has shortcomings in that much cost and time are required and it is difficult to form the anti-reflective structure over a large area on a spherical surface.
Thus, it is preferable to a novel method capable of making a plastic lens having an anti-reflective structure, which overcomes the problems of the above-described conventional lithography-based method and can produce the plastic lens in large amounts. However, an apparatus or a method, which satisfies all the above-described requirements, has not yet been provided.
Accordingly, the present inventors have conducted studies to develop a lens having decreased reflectance, increased transmittance and high efficiency, and as a result, have found that, when an anti-reflective layer having nano-structures is formed on the lens surface, a lens can be produced in a simple manner in large amounts, thereby completing the present invention.